Micro-cantilever sensing systems have become popular tools for detecting properties of various fluids, including for use in detecting the presence of analytes in a particular fluid. Such micro-cantilever sensing systems are generally capable of measuring nanoscale deflections, nanomechanical resonances, and, in some cases, Q-factors of micro-cantilevers. In general, micro-cantilever systems utilize the concept that physical, chemical, or biological stimuli can affect the mechanical characteristics of a micro-cantilever in such a way that the resulting change can be measured using optical, electronic, and other sensing devices. Thus, by measuring a given physical aspect of a micro-cantilever, such as magnitude of deflection or vibratory frequency, some physical, chemical or biological aspect of the fluid in which the micro-cantilever is disposed can be detected or monitored.
In some exemplary cases, one side (or sometimes, both sides) of a micro-cantilever beam is “functionalized,” e.g. treated to absorb or react with a particular analyte in a fluid, such that the absorption or reaction causes the behavior of the micro-cantilever within the fluid to change. Generally, the absorption or reaction causes an increase in mass of the micro-cantilever, which results in some change in physical response of the cantilever. Monitoring this change in response of the micro-cantilever can indicate, for example, the presence or concentration of a particular analyte in the fluid at issue. Micro-cantilever systems can include both “static” systems, which generally measure cantilever deformation as a means of monitoring absorption or reaction with an analyte, and “dynamic” systems, which generally measure resonance frequency of the micro-cantilever to monitor absorption or reaction with an analyte.
In general, dynamic micro-cantilever systems are often more sensitive to minute changes in behavior of a micro-cantilever and are thus preferred in many applications over static micro-cantilevers. However, as the sensitivity of a dynamic micro-cantilever system often depends upon the quality factor (or “Q”) of the micro-cantilever, dynamic systems do not often perform well in systems in which a fluid with a relatively high viscosity is used. This is due to the fact that a relatively high viscosity fluid will dampen the reaction of the micro-cantilever, thereby reducing the Q and the sensitivity of the cantilever. While some systems have attempted to compensate for this condition and utilize dynamic micro-cantilevers in liquids, such systems have required the use of sophisticated active feedback control systems to counter the highly damped signal.